2. Parts Wellhead
All casing strings, except for liners, are suspended from a wellhead.
On a land well or offshore platform the wellhead is just below the rig floor.
When drilling offshore, from a floating vessel, the wellhead is installed at the seabed.
The wellhead on a land or platform well is made up of a series of spools, stacked up, one on top of the other.

3. Parts Wellhead Surface wellhead spools have four functions:
To suspend the weight of the casing string;
To seal off the annulus between successive casing strings at the surface;
To allow access to the annulus between casing strings;
To act as an interface between the casing string and BOP stack.

4. Parts Wellhead

5. Parts Wellhead

6. Parts Wellhead
Slip Type Casing Hangers: This type of hanger is wrapped around the casing and then lowered until it sits inside the casing spool. The slips are automatically set when the casing is lowered. This type of hanger can be used if the casing stands up on a ledge and cannot reach its required setting depth. These types of hanger are also used when tension has to be applied in order to avoid casing buckling when the well is brought into production.

7. Parts Wellhead
Mandrel Type Casing Hangers: is screwed onto the top of the casing string so that it lands in the casing housing when the casing shoe reaches the required depth.
Although this is the most common type of hanger it cannot be used if there is a risk that the casing will not reach bottom and therefore that the hanger will not land in the wellhead.

8. Parts Wellhead
Casing spool is a well head component used in flanged wellhead assemblies to secure the upper end of a casing string.
Casing spools or bowls are available in a wide range of sizes and pressure ratings and are selected to suit the specific conditions.

9. Parts Wellhead
The procedure for installing a spool type wellhead system can be outlined as follows
Conductor (20’’) is run and cemented in place
Surface casing (13 5/8’’) is run and cemented in place. A casing head housing is welded onto the top of the surface casing. BOP is connected to the upper flange of the housing.
Intermediate casing (8 5/8’’) is run and cemented in place. BOP is disconnected and a casing spool is flanged up on the top of the surface casing. Casing hanger is run into the casing housing. The BOPs made up on the top of the spool.
The process continues with a new spool being installed for each casing string
Finally the Christmas tree is installed on the top of the wellhead.

10. Parts Wellhead

11. Parts Wellhead
Christmas tree (NOT a wellhead) is an assembly of valves, spools, and fittings used for an oil, gas wells, water injection well, water disposal well, and gas injection well. It is installed on the top of the wellhead.
The primary function of a tree is to control the flow of oil or gas.
A tree often provides numerous additional functions including:
Chemical injection
Well intervention means
Pressure relief means
Monitoring points: pressure, temperature, corrosion, erosion, …
Connection points for devices: down-hole pressure and temperature